This invention relates to a developer material coating apparatus for coating a support member such as a plain paper with granular developer material, and more particulary to a developer material coating apparatus having a coating amount control unit for freely adjusting the amount of the developer material to be coated on the support member.
There has been recently utilized a color copying machine in which a color image is formed on a support member such as plain paper using granular developer material and a microcapsule sheet. A color image forming process of this type of color copying machine is as follows. A developer sheet is beforehand formed by coating the developer material on the support member such as plain paper, and the microcapsule sheet is exposed through an original to light to form a latent image on the microcapsule sheet. The microcapsule sheet having the latent image thereon and the developer sheet comprising the support member coated with the developer material are fed to a pressure-developing unit while contacted with each other. In the pressure-developing unit, the microcapsule sheet and the developer sheet are subjected to a pressure-developing process to develop the latent image on the microcapsule sheet into a visible color image on the developer sheet. Thereafter, the developer sheet having the visible color image thereon is fed to a heat-fixing unit to thermally fix the visible color image on the developer sheet. The developer material is formed of , for example, acid clay, binder and so on, and thus the developer sheet may comprise the support member coated with the developer material formed of the acid clay, the binder and so on.
As described above, this type of color copying machine requires a process for coating the developer material on the support member such as plain paper, and thus a coating apparatus therefor. As a coating apparatus, there has been conventionally used a coating apparatus in which the developer material on the support member is charged with triboelectrification and then is electrostatically coated on the support member.
FIG. 1 shows a conventional coating apparatus for coating the developer material on the support member such as plain paper. This coating apparatus comprises, for example, a support member feeding unit for feeding the support member to a developer material coating region in which the support member is electrostatically coated with the developer material and then discharging the support member coated with the developer material to an outside of the coating apparatus, and a developer material coating unit for triboelectrically charging the developer material and electrostatically coating the charged developer material on the support member.
The developer material coating unit comprises a tank (hopper) 50 for accommodating the developer material S therein, a carry roller 52 for carrying the developer material thereon and a supply roller 51 for triboelectrically charging the developer material in cooperation with the carry roller 52 and supplying the charged developer material to the carry roller 52. The carry roller 52 is grounded as shown in FIG. 1. The carry roller 52 and the supply roller 51 are rotatably contacted with each other at the peripheral surfaces thereof, and the developer material S is triboelectrically charged at a predetermined polarity (positively or negatively) at the contacted surfaces of the rollers 51 and 52 through a friction between the surface of the carry roller 52 and the developer material S. The charged developer material S is attached to peripheral surface of the carry roller 52 and then is fed to the developer material coating region while carried on the carry roller.
The support member feeding unit comprises a counter electrode roller 53, which is supplied with a voltage having the opposite polarity to that of the charged developer material from a D.C. power source, a pair of guide rollers 55 provided away from the counter roller 53 and a carry belt 54 such as an endless belt for feeding the support member to the developer material coating region while carrying the support member P thereon and discharging the support member coated with the developer material (developer sheet) to the outside of the coating apparatus, the carry belt 54 being suspended among the counter roller 53 and the guide rollers 55 and 56. In FIG. 1, since the developer material S is positively charged, the counter electrode roller 53 is supplied with a negative voltage.
The support member P carried on the carry belt 54 is fed to the developer material coating region by the rotation of the counter roller 53 and the guide rollers 55. The positively-charged developer material S on the carry roller 52 is electrostatically attracted toward the counter electrode roller 53 due to an electric field which is caused between the counter roller 53 having a positive potential and the grounded carry roller 52. That is, particles of the positively-charged developer material S is electrostatically attracted (flight) toward the counter electrode roller 53 in the developer material coating region where the counter roller 53 and the carry roller 52 are confronted to each other, and attach to the support member P to form a developer material layer m on the support member P, that is, a developer sheet.
In a practical use of the image forming apparatus including the developer material coating apparatus thus constructed, it is required to accurately and stably obtain an visible image corresponding to an original image that a constant or optimum amount of the developer material P be constantly coated on the support member P, that is, a constant or optimum thickness of the developer material S be coated on the support member P, irrespective of characteristics of the support member such as kind, thickness and surface condition of the support member and environmental conditions such as temperature, humidity and so on. However, the above conventional developer material coating apparatus, as described below, has not been satisfied for the above requirements.
For example, in the conventional developer material coating apparatus, an amount of the developer material S to be coated on the support member P (hereinafter referred to as "a coating amount") is changed in accordance with the change of the temperature or the humidity within the coating apparatus. In general, a charging amount of the developer material S is changed in accordance with the change of temperature, humidity or the like, and the change of the charging amount of the developer material S causes the change of an amount of the developer material to be carried on the carry roller and thus coated on the support member. For example, if the humidity in the coating apparatus rises in accordance with increase of the temperature in the coating apparatus, then the charging amount of the developer material S is decreased, and therefore the thickness of the developer material layer m on the support member P is smaller than that of the developer material layer m coated on the support member P at a room temperature. That is, the coating amount of the developer material S on the support member P is changed in accordance with the change of the temperature or the humidity, and thus a stable image can not be constantly obtained.
Further, in the conventional developer material coating apparatus, the coating amount of the developer material S on the support member P is changed in accordance with the thickness of the support member P for the following reason. The distance of a gap between the carry roller 52 and the support member P which is fed to the developer material coating region is changed in accordance with the thickness of the support member P itself, and the change in the distance of the gap causes the change of the amount of the developer material S to be coated on the support member P. As a result, a constant thickness of the developer material layer m can not be obtained on the support members having different thicknesses.
Still further, in the conventional developer material coating apparatus, an amount (or thickness) of the developer material to be coated on any kind of support member can not be changed in accordance with the kind of the support member or a surface condition (for example, a rough surface, a flat surface or the like) of the support member. Therefore, irrespective of the differences in the kind of the support member and the surface condition thereof, the same amount of the developer material has been constantly coated on any kind of support member such as a rough sheet having a rough surface of a rough fiber arrangement, a plastic sheet such as an OHP sheet having a flat surface and so on. Therefore, it easily occurs in some kinds of support members that the image surface on each of the support members becomes rough, and the developer material on the support member after pressure-developed is exfoliated from the support member to damage the image on the support member.